1. Field of the Invention
The present invention relates to an alternator for motor vehicles which has a mounting structure suitable for mounting to an engine.
2. Description of the Prior Art
FIG. 1 is a view showing the appearance of a conventional alternator for motor vehicles. A front bracket 1 is provided integrally with a lower flange 2a and an upper flange 2b which are projecting sections for mounting. The lower flange 2a is provided with lower mounting bosses 4a and 4b having mounting bolt holes 3a and 3b which are drilled in a direction perpendicular to the direction of the axis of rotation, and through which mounting bolts not illustrated are inserted to fixedly tighten the alternator for motor vehicles to an engine not shown. The upper flange 2b is also provided with an upper mounting boss 4c having a mounting hole 3c drilled in a direction perpendicular to the direction of the axis of rotation. Numeral 5 denotes a stator, which is partly fitted between the front bracket 1 and a rear bracket 6 and securely fastened by through bolts 7. A flange 8 formed integral with this rear bracket 6 is fixedly mounted by a bolt 10 to the lower flange 2a through a bushing 9. Numeral 11 is a pulley for transmitting the rotation of the engine not shown, through a belt, to a rotor not shown which is rotatably supported inside of the alternator for motor vehicles.
The front bracket 1 and the rear bracket 6 described above are commonly produced by casting. After casting, those parts which require dimensional accuracy, for example the mounting bolt holes 3a, 3b and 3c and the mounting bosses 4a, 4b and 4c, are machined and used. As well known, in casing extremely long and thick parts, such problems as cavities or shrinkage are likely to occur. In machining, a better efficiency is obtainable by machining only in one direction.
In the mounting structure of the alternator for motor vehicles described above, cavities or shrinkage are likely to occur in casting the lower flange 2a having particularly long-pitch mounting bolt holes 3a and 3b. As regards the machining of the mounting holes 3a, 3b and 3c and the mounting bosses 4a, 4b and 4c, other parts of the brackets such as the through holes through which the bolts 7 are mounted and a section to be fitted to the stator 5 are machined in the axial direction of the alternator for motor vehicles. In this case, however, the machining is done in a direction perpendicular to the axial direction, with the result that the machining efficiency will become lowered and also, plural chucking operations will be required during machining.
The mounting structure of the conventional alternator for motor vehicles is inferior because of excessively deteriorated vibration resistance and strength caused by the presence of cavities or shrinkage occurring during casting or a lowered dimensional accuracy of machining. This alternator, therefore, has presented a secondary problem such as an off centered pulley when mounted on an engine and driven.